Organic Light Emitting diodes (OLED) devices are comprised of two electrodes and an organic light emitting layer. The organic layer is disposed between the two electrodes. One electrode is the anode and the other electrode is the cathode. The organic layer is structured such that when the anode has a voltage bias that is sufficiently positive relative to the cathode, holes are injected from the anode and electrons are injected from the cathode. The necessary voltage bias depends upon the materials used for the organic layers. The holes and electrons recombine within the organic layer to induce an exited state in a molecule comprising the organic layer. Light is emitted during the process of excited molecules relaxing to their ground state. The anode is typically manufactured from a high work function material such as a Transparent Conducting Oxide (TCO), and the cathode is typically manufactured from a highly reflecting material such as aluminum or silver. However, there exist many different electrode designs which allow light to exit the cathode, the anode, or through both the cathode and the anode. The organic layer can be comprised of a single organic film, or it can be comprised of a stack of multiple organic films. OLED devices are useful as indicators and displays can be constructed from patterned arrays of OLED devices.
In conventional capacitive touch sensors, a touch is detected by detecting the change in capacitance between an electrode and ground. The change in the capacitance necessary to trigger a touch response needs to be determined in advance. However, environmental conditions (e.g. the humidity) can affect the capacitance of the electrode to ground and make it difficult to determine the proper change in capacitance that will work for all conditions.
A more sophisticated type of capacitive touch sensor is the Near Field Imaging (NFI) or gradient touch sensor. NFI sensors are typically constructed from a minimum of three layers. There is a bottom dielectric substrate, there is a layer of conductive elements mounted on the dielectric substrate, and there is another dielectric layer mounted on the conductive elements which serve to protect the conductive elements. Each of the conductive elements is adapted to conduct current, and are supplied with a Radio-Frequency (RF) voltage. The current flowing through each element is detected. As an object approaches the NFI sensor the capacitance of the individual conductive elements changes and causes a change in the measured currents.
The change in capacitance can be due to an increase or decrease in the capacitance of the individual conductive elements to ground or they can be due to changes in the electric field caused by the approaching object. Both conductive objects and dielectric objects will cause a change in the capacitance between individual elements. Some elements have their capacitance and hence the measured current change more than others. These localized changes in the current allow the location of the touch to be inferred. The elements which are affected less by the approaching object can be used as a reference compare against when determining the threshold for when a touch has occurred.
PCT Patent WO 2004/010369 discloses a combined Liquid Crystal Display (LCD) screen and NFI touch screen.